1. Field of the Invention
The present invention relates to a communication system, and a multiplexer included in the system, a line performance test method and a recording medium having a program recorded thereon, and in particular, to the communication system of an ADSL (Asymmetric Digital Subscriber Line) line, and the multiplexer included in the system, line performance test method and recording medium having a program recorded thereon.
2. Description of the Prior Art
ADSL is a modem technology for allowing high-rate data communication of several Mbps at the maximum by utilizing an existing subscriber line, that is, a telephone line (copper wire) mainly used for a telephone.
The ADSL is standardized as “G. dmt”by the ITU-T recommendation G. 992.1 and as “G. lite” by the ITU-T recommendation G. 992.2. The ADSL is one of the methods of xDSL which is the modem technology, and the xDSL is a generic term for Asymmetric DSL (Digital Subscriber Line), High-bit-rate DSL, Rate-Adaptive DSL, Symmetric DSL and Very-high-bit-rate DSL.
High-speed Internet access by always-on connections becomes possible for a subscriber by using this ADSL line service.
However, the ADSL is characterized in that its performance and data communication rate are influenced by a distance of a subscriber line to be the ADSL line, that is, a telephone line, line characteristics and ambient surrounding conditions of the line from a telephone office to the subscriber's house.
Therefore, the data communication rate of the ADSL line service is different for each of the subscribers. The data communication rate is generally called a line rate or an acquired band of the ADSL line. In the case of the ADSL, the acquired bands are asymmetric between an up stream direction from the subscriber to a network and a down stream direction from the network to the subscriber.
The acquired band is determined by training results standardized by G. dmt and G. lite. As for the ADSL, there are the cases where the ADSL line is cut if the telephone line is influenced by impulse-like noise from the outside. Data transmission is interrupted in this state of the ADSL line.
However, the ADSL line recovers automatically by performing the training again. Representative parameters of ADSL line configuration parameters are an ADSL line rate (normally represented as Mbps), an SNR (Signal to Noise Ratio) margin and an interleave delay.
The SNR margin is the ADSL line configuration parameters for showing a bearing force against the noise from the outside. The SNR margin parameters are further classified into a target SNR margin, a maximum SNR margin and a minimum SNR margin.
The interleave delay is the ADSL line configuration parameter for showing the time required when performing a prescribed error correcting code function by scrambling a data signal flowing on the ADSL line, and it is sometimes utilized as the ADSL line configuration parameter for setting reliability of the data signal which also shows a buffer amount to temporarily store the data signal for the sake of performing the error correcting code function.
The acquired band of the ADSL line, that is, the ADSL line rate is the parameter for showing the line rate determined by the ADSL training according to the SNR, interleave delay and ambient surrounding.
It is also the line configuration parameter for, by inversely specifying the ADSL line rate, rendering a specified value as the ADSL line rate.
The ADSL line configuration parameters of the ADSL line rate, SNR margin and interleave delay are set in both the up stream and the down stream directions of the ADSL line respectively.
There is a correlation among the ADSL line configuration parameters of the ADSL line rate, SNR margin and interleave delay, where the ADSL line rate is reduced if the SNR margin is increased and the ADSL line rate is increased if the SNR margin is reduced.
In addition, the ADSL line rate is reduced if the interleave delay is increased, and the ADSL line rate is increased if the interleave delay is reduced.
Furthermore, in the case where a subscriber line distance is short, that is, the subscriber's house is near the telephone office, the SNR margin can be increased, and in the case where the subscriber line distance is long, that is, the subscriber's house is distant from the telephone office, the SNR margin is reduced so as to link up the ADSL line.
To be more specific, there is a close relationship among the ADSL line rate, subscriber line distance, SNR margin, interleave delay and ambient surrounding, and in the case of providing the ADSL line service, it is necessary to adjust (customize) these parameters.
FIG. 13 is a block diagram of a DSLAM (Digital Subscriber Line Access Multiplexer) in the past for providing such ADSL line service. A DSLAM1000 in the past is comprised of a data signal multiplexing portion 3, an ATU-C (ADSL Termination Unit—Central Office: an office side ADSL modem) #1 100a, an ATU-C #2 100b, an ATU-C #n (n is a positive integer) 100n and an ADSL line initial value setup portion 9.
The data signal multiplexing portion 3 multiplexes data signals received from the ATU-C #1 100a, ATU-C #2 100b and ATU-C #n 100n and sends them to a network 90. The data signal multiplexing portion 3 also sends the data signals received from the network 90 by sorting them into the ATU-C #1 100a, ATU-C #2 100b and ATU-C #n 100n. 
The ADSL line initial value setup portion 9 has a preset ADSL line configuration parameter initial value, and sets the parameter to the ATU-C #1 100a, ATU-C #2 100b and ATU-C #n 100n respectively.
At the subscriber's house, an ATU-R (ADSL Termination Unit—Remote: a subscriber side ADSL modem) #1 200a, an ATU-R #2 200b, an ATU-R #n 200n and a PC (personal computer) #1 300a, a PC #2 300b and a PC #n 300n held by the subscribers respectively are installed. The respective PC #1 300a, PC #2 300b and PC #n 300n are connected to the ATU-R #1 200a, ATU-R #2 200b and ATU-R #n 200n respectively.
The respective ATU-C #1 10a, ATU-C #2 100b and ATU-C #n loon in the DSLAM1000 are connected to the respective ATU-R #1 200a, ATU-R #2 200b and ATU-R #n 200n via the respective subscriber lines 500a, 500b and 500n. 
The ADSL is a technology for allowing high-rate data communication by utilizing an existing telephone line, and so the respective subscriber lines 500a, 500b and 500n to the subscriber's house are the telephone lines currently in use, which will be the ADSL lines.
The subscribers use their respective PC #1 300a, PC #2 300b and PC #n 300n to connect to the network 90 via the ATU-R #1 200a, ATU-R #2 200b and ATU-R #n 200n, the subscriber lines 500a, 500b and 500n which are now the ADSL lines capable of the high-rate data communication and the DSLAM1000 so as to perform the data communication related to the Internet.
Next, operation of the DSLAM in the past will be described. FIG. 14 is a flowchart showing the operation of the ADSL line setup of the DSLAM in the past (1000 in FIG. 13), that is, a start of the ADSL line service provision.
First, it is determined whether or not preparations for starting the operation have been made (step B1). At first, it is determined that the preparations have not been made because the ADSL line service is in an inoperative state (NO in the step B1). Next, the DSLAM (1000 in FIG. 13) prepares the ADSL line configuration parameter initial value held in advance (step B2). Next, the ADSL line initial value setup portion (9 in FIG. 13) sets the ADSL line configuration parameter initial value to the respective ATU-C #1 100a, ATU-C #2 100b and ATU-C #n loon (step B3).
Here, it means that the ATU-Cs have a common unique ADSL line configuration parameter set up thereon. Then, the ATU-Cs (the ATU-C #1 100a, ATU-C #2 100b and ATU-C #n 100n in FIG. 13) refer to the ADSL line configuration parameter set up in the step B3 to perform the training with the ATU-Rs (the ATU-R #1 200a, ATU-R #2 200b and ATU-R #n 200n in FIG. 13) in compliance with G. dmt or G. lite. As a result of the training, the ADSL lines are linked up (YES in the step B4).
The service allowing high-rate data communication is provided by the linked up ADSL lines (step B5). And if the subscriber is satisfied with the ADSL line state and quality (YES in the step B6), then the ADSL lines will be in a service operation state (step B7).
However, there are the cases where the ADSL lines are not linked up with the ADSL line configuration parameter initial value in the step B2 (NO in the step B4) and the cases where the subscriber may feel dissatisfied such as synchronization of the ADSL lines sometimes being cut and the data communication being interrupted due to the state of the ADSL lines of the subscriber, that is, the rate of the acquired bands and the influence of a noise source halfway on the line to the subscriber's house (NO in the step B6). In such cases, the subscriber files a claim to the ADSL line service provider (step B10).
As opposed to this, the ADSL line service provider determines that the ADSL lines are in the state of starting the operation (YES in the step B1). And the ADSL line service provider examines and adjusts the ADSL line configuration parameter conforming to the lines of the subscriber filing the claim (step B8), and sets up the ADSL line configuration parameter adjusted in the step B8 on the ATU-Cs to which the ADSL lines of the subscriber are connected (step B9).
And the training is performed again (step B4 and B5). If the subscriber is satisfied with the ADSL line state and quality as-is (YES in the step B6), then the ADSL lines will be in the service operation state (step B7). If the subscriber is not satisfied with the ADSL line state and quality as-is (NO in the step B6), then the processing of the steps B1 to B6 is repeated from the step B10.
A first problem of the DSLAM in the past is that, as an optimum ADSL line configuration parameter to each subscriber line is not set up, the lines of inferior quality as the ADSL lines are generated.
The reason for it is that, although each line of the subscriber lines in which the ADSL lines are linked up is influenced by each individual ambient surrounding, the DSLAM adapts the same ADSL line configuration parameter initial value to any subscriber line.
To be more specific, it is because the ADSL line configuration parameter initial value held by the DSLAM is not necessarily the optimum ADSL line configuration parameter for implementing an optimum ADSL line performance of the subscriber line. For this reason, there may occur a state in which the ADSL line of a certain subscriber is so often interrupted that normal data communication cannot be performed.
A second problem is that work by a maintenance worker is necessary to adjust the ADSL line configuration parameter and expenses for the human work arises accordingly.
The reason for it is that the ADSL line configuration parameter needs to be adjusted according to presumption and rules of experience of the maintenance worker of the ADSL line service provider in order to link up the ADSL line and provide a satisfactory ADSL line state and quality to the subscriber.
A third problem is that it takes time to handle the claims from the subscribers.
The reason for it is the same as that for the second problem.
A fourth problem is that maintainability of the ADSL line is inferior because the ADSL line service provider cannot always hold the optimum ADSL line configuration parameter according to the change in the ambient surrounding of the subscriber line.
The reason for it is that the DSLAM holds only the ADSL line configuration parameter initial value as with the first problem and that man-hours arise due to the human work as with the second problem.
Japanese Patent Laid-Open No. 2000-209338 discloses a technology relating to a method of testing a communication link for high-rate services, which is the technology for testing electrical and/or physical properties of the lines. To be more specific, it is the technology for testing a loop length, a line load impedance, a load coil, a frequency characteristic and so on.
As opposed to this, the present invention is the technology for testing the performances of the lines, which is entirely different from the technology described in the above patent laid-open as to all of the object, configuration, action and effects.
Thus, an object of the present invention is to provide a communication system capable of providing the optimum ADSL line configuration parameter to each subscriber line and improving the ADSL line performance quality, a multiplexer included in the system, a line performance test method and a recording medium having program recorded thereon. Another object of the present invention is to realize improvement in working efficiency and reduction in costs of adjustment of the ADSL line configuration parameter for specific subscriber lines.
A further object of the present invention is to be able to immediately handle the claims from the subscribers, subscriber line environment and so on and improve the maintainability, reliability and customer satisfaction of the ADSL line service.